1. Field of the Invention
The present invention relates to a semiconductor device such as an IGBT (Insulated Gate Bipolar Transistor) having a bidirectional breakdown voltage and a manufacturing method thereof, and more particularly to a peripheral breakdown voltage structure in the semiconductor device.
2. Description of the Background Art
In recent years a power conversion circuit, the so-called AC matrix converter, which is switched on and off directly by a bidirectional switch has been proposed to be used in a semiconductor power conversion device. And a semiconductor device having a bidirectional breakdown voltage has been called for as the bidirectional switch used in the AC matrix converter.
One conventional example of such semiconductor device is a reverse blocking IGBT as illustrated in FIG. 1 of Japanese Patent Application Laid-Open No. 2002-319676 (pages 7 to 8, FIG. 1). This kind of reverse blocking IGBT, however, requires a p+ region obtained by diffusing boron to a depth of 120 μm in an oxygen atmosphere at a temperature of 1200° C. or more to lie on the periphery of a chip in order to maintain a reverse breakdown voltage, and thus needs a long-diffusion process. Besides, horizontal diffusion of the boron causes the p+ region to spread over a chip surface to the almost same degree as the diffusion depth, resulting in a considerable reduction in utilization efficiency of the chip surface.
In order to address those problems, Japanese Patent Application Laid-Open No. 2001-185727 (page 7, FIG. 15) proposes a reverse blocking IGBT having such a structure as shown in FIG. 15(c). This IGBT provides an inclined trench in a portion corresponding to the p+ region of the IGBT disclosed in the aforementioned publication using side etching by isotropic wet etching to form a positive bevel structure, and introduces an impurity by diffusion from a wall surface of the trench to provide p+ regions. While this IGBT eliminates the need for a long-diffusion process as in the IGBT disclosed in the aforementioned publication, it does need a trench width in accordance with the inclination because the trench needs to be inclined. This too has considerably reduced utilization efficiency of a chip surface.
The terminal structures disclosed in the Japanese Patent Application Laid-Open Nos. 2002-319676 and 2001-185727 both require a considerable area of the chip to form the structure for maintaining the reverse breakdown voltage, resulting in a considerable reduction in utilization efficiency of the chip surface. This has caused an increase in chip size, which in turn has increased the chip cost.